ACPI: move acpi_no_s4_hw_signature() declaration into #ifdef CONFIG_HIBERNATION

acpi_no_s4_hw_signature is defined in #ifdef CONFIG_HIBERNATION block,
but the current code put the declaration in #ifdef CONFIG_PM_SLEEP block.

I happened to meet this issue when I turned off PM_SLEEP config manually:
arch/x86/kernel/acpi/sleep.c:100:4: error: implicit declaration of function ‘acpi_no_s4_hw_signature’ [-Werror=implicit-function-declaration]

Signed-off-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>
Reviewed-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>